Permeability of media composed of impenetrable cylinders covered with porous layer

The liquid flow through a set of nonuniform porous cylinders with a impenetrable core are studied by the Happel—Brenner cell method. Different orientations of cylinders relative to the liquid flow, such as transverse, longitudinal, and random, are considered. Brinkman equations are used to describe the flow of liquid in the porous layer. All known boundary conditions on the cell surface (Happel, Kuwabara, Kvashnin, and Cunningham conditions) are considered. The models proposed can be used to describe the processes of reverse osmosis, as well as nano-and ultrafiltration.     

First and second laws of thermodynamics analysis of nanofluid flow inside a heat exchanger duct with wavy walls and a porous insert

This paper investigates the combined effects of using nanofluid, a porous insert and corrugated walls on heat transfer, pressure drop and entropy generation inside a heat exchanger duct. A series of numerical simulations are conducted for a number of pertinent parameters. It is shown that the waviness of the wall destructively affects the heat transfer process at low wave amplitudes and that it can improve heat convection only after exceeding a certain amplitude. Further, the pressure drop in the duct is found to be strongly influenced by the wave amplitude in a highly non-uniform way. The results, also, show that the second law and heat transfer performances of the system improve considerably by thickening the porous insert and decreasing its permeability. Yet, this is associated with higher pressure drops. It is argued that the hydraulic, thermal and entropic behaviours of the system are closely related to the interactions between a vortex formation near the wavy walls and nanofluid flow through the porous insert. Viscous irreversibilities are shown to be dominant in the core region of duct where the porous insert is placed. However, in the regions closer to the wavy walls, thermal entropy generation is the main source of irreversibility. A number of design recommendations are made on the basis of the findings of this study.

     

Electrophoretic mobility of a charged cylindrical colloidal particle covered with an ion-penetrable uncharged polymer layer

Expressions are derived for the electrophoretic mobility of a cylindrical charged colloidal particle carrying a low zeta potential covered with an ion-penetrable uncharged polymer layer in an electrolyte solution. These expressions involve numerical integration of modified Bessel functions but are easily calculable with Mathematica. The obtained mobility expressions are a modification of Henry's mobility formula for a cylindrical particle taking into account the presence of the uncharged polymer layer.     

Electrokinetic flow in a capillary with a charge-regulating surface polymer layer

An analytical study of the steady electrokinetic flow in a long uniform capillary tube or slit is presented. The inside wall of the capillary is covered by a layer of adsorbed or covalently bound charge-regulating polymer in equilibrium with the ambient electrolyte solution. In this solvent-permeable and ion-penetrable surface polyelectrolyte layer, ionogenic functional groups and frictional segments are assumed to distribute at uniform densities. The electrical potential and space charge density distributions in the cross section of the capillary are obtained by solving the linearized Poisson-Boltzmann equation. The fluid velocity profile due to the application of an electric field and a pressure gradient through the capillary is obtained from the analytical solution of a modified Navier-Stokes/Brinkman equation. Explicit formulas for the electroosmotic velocity, the average fluid velocity and electric current density on the cross section, and the streaming potential in the capillary are also derived. The results demonstrate that the direction of the electroosmotic flow and the magnitudes of the fluid velocity and electric current density are dominated by the fixed charge density inside the surface polymer layer, which is determined by the regulation characteristics such as the dissociation equilibrium constants of the ionogenic functional groups in the surface layer and the concentration of the potential-determining ions in the bulk solution.     

A capillary gas chromatographic column with a porous layer based on a mesoporous material

A procedure for synthesizing an MSM-41-type mesoporous mesophase material (MMM) layer, that is, a layer of a solid porous material with a regular arrangement of nanoscale calibrated pores and a unified geometry, on the inner wall of a capillary column was developed. Because of the high specific surface area of silica, capillary columns with a porous MMM layer on the basis of silica allow the amount of samples introduced to be increased by an order of magnitude compared with the known capillary porous-layer columns. An example of the separation of light hydrocarbons is described. The properties of columns with MMM porous layers are discussed.     

Electrostatic potential and electroosmotic flow in a cylindrical capillary filled with symmetric electrolyte: analytic solutions in thin double layer approximation

The electrostatic potential in a capillary filled with electrolyte is derived by solving the nonlinear Poisson-Boltzmann equation using the method of matched asymptotic expansions. This approach allows obtaining an analytical result for arbitrary high wall potential if the double layer thickness is smaller than the capillary radius. The derived expression for the electrostatic potential is compared to numerical solutions of the Poisson-Boltzmann equation and it is shown that the agreement is excellent for capillaries with radii greater or equal to four times the electrical double layer thickness. The knowledge of the electrostatic potential distribution inside the capillary enables the derivation of the electroosmotic velocity flow profile in an analytical form. The obtained results are applicable to capillaries with radii ranging from nanometers to micrometers depending on the ionic strength of the solution.     

Entropy generation analysis for nanofluid flow inside a duct equipped with porous baffles

Journal of Thermal Analysis and Calorimetry - In this research, a numerical simulation is performed to investigate thermal and viscous irreversibilities for Al2O3–water nanofluid inside a...     

A capillary gas chromatographic column with a porous layer based on the divinylbenzene-vinylimidazole copolymer

Capillary columns with a new sorbent based on the divinylbenzene-vinylimidazole organic copolymer are proposed. The properties of the prepared columns are discussed. It is demonstrated that columns based on the divinylbenzene-vinylimidazole polymer with different selectivities can be prepared by varying the relative amount of vinylimidazole in the initial polymerization mixture. The examples of separation of light hydrocarbons, permanent gases, and oxygen-containing compounds are given.     

Cell models for flows in concentrated media composed of rigid impenetrable cylinders covered with a porous layer

Absract  The hydrodynamic permeability of a membrane simulated by a set of identical impenetrable cylinders covered with a porous layer is calculated by the Happel-Brenner cell method. Both transverse and longitudinal flows of filtering liquid with respect to the cylindrical fibers that compose the membrane are studied. Boundary conditions on the cell surface that correspond to the Happel, Kuwabara, Kvashnin, and Cunningham models are considered. Brinkman equations are used to describe the flow of liquid in the porous layer. Results that correspond to previously published data are obtained for the limiting cases. Theoretical values of Kozeny constants are calculated. The models proposed can be used to describe the processes of reverse osmosis, as well as nano- and ultrafiltration. Original Russian Text ? S.I. Vasin, A.N. Filippov, 2009, published in Kolloidnyi Zhurnal, 2009, Vol. 71, No. 2, pp. 149–163.     

Cell lysis inside the capillary facilitated by transverse diffusion of laminar flow profiles (TDLFP)

Chemical cytometry studies the molecular composition of individual cells by means of capillary electrophoresis or capillary chromatography. In one of its realizations an intact cell is injected inside the capillary, the plasma membrane is disrupted to release the cellular contents into the separation buffer, and, finally, the molecules of interest are separated and detected. The solubilization of the plasma membrane with a surfactant is a simple and efficient way of achieving cell lysis inside the capillary. To facilitate cell lysis by a surfactant the cell has to be contacted with the surfactant inside the capillary. We recently introduced a generic method for mixing solutions inside the capillary termed transverse diffusion of laminar flow profiles (TDLFP). In this work, we propose that TDLFP can facilitate efficient cell lysis inside the capillary. Conceptually, a short plug of the surfactant is injected by pressure prior to cell injection. The cell is then injected by pressure wizthin a plug of the physiological buffer. Due to the parabolic profiles of pressure-driven laminar flows the interface between the plug of the surfactant and that of the physiological buffer is predominantly longitudinal. Transverse diffusion mixes the surfactant with the physiological buffer, which leads to surfactant’s contact with the cell and subsequent cell lysis. Here, we demonstrate that the proposed concept is valid. TDLFP-facilitated cell lysis by a short plug of the surfactant allows us to exclude the surfactant from the run buffer, and, hence, facilitates modes of separation, which are incompatible with the surfactant’s presence in the run buffer. In addition to cell lysis, TDLFP will be used to mix the cellular components with labeling reactants, affinity probes, inhibitors, etc. We foresee that the generic nature and enabling capabilities of TDLFP will speed up the maturation of chemical cytometry into a practical bioanalytical tool.     

Multi-gradient hydrogels produced layer by layer with capillary flow and crosslinking in open microchannels

This technical note describes a new bench-top method for producing anisotropic hydrogels composed of gradient layers of soluble factors, particles, polymer concentrations or material properties. Each gradient layer was produced by a previous gradient method in which a droplet of one precursor solution was added to a thin layer of a second solution. The ensuing rapid capillary flow along the open channel generated a gradient precursor solution, which was then crosslinked to form a gradient gel. Repeating these steps allowed a layered gel to be iteratively constructed with as many gradient layers as desired. This technique renders the synthesis of multi-layered gradient gels accessible to virtually any researcher and should help simplify the production of more biologically relevant cellular microenvironments.     

Open-tubular capillary columns with a porous layer of monolithic polymer for highly efficient and fast separations in electrochromatography

Open-tubular columns for CEC separations having inner-wall coated with a thin layer of porous monolithic polymer have been studied. A two-step process including (i) UV-initiated polymerization leading to a layer of porous poly(butyl methacrylate-co-ethylene dimethacrylate), and (ii) UV-initiated grafting of ionizable monomers appear to be well suited for the preparation of these columns. The thickness of the porous polymer layer is controlled by the percentage of monomers in the polymerization mixture and/or length of the irradiation time. The layer thickness significantly affects retention, efficiency, and resolution in open-tubular CEC. Under optimized conditions, column efficiencies up to 400,000 plates/m can be achieved. Use of higher temperature and application of pressure enables a significant acceleration of the open-tubular CEC separations.     

Simulation of thermal radiation in a micropolar fluid flow through a porous medium between channel walls

Journal of Thermal Analysis and Calorimetry - Among numerous methods which have been employed to reinforce the thermal efficiency in many systems, one is the thermal radiation which is a mode of...     

The use of vacuum in thin-layer chromatography with a forced flow of the mobile phase on plates with covered polymer layer

A new version of TLC with a forced flow of the mobile phase has been suggested. The variant involves the use of a TLC plate, the sorption layer on which is covered with a polymer film, and evacuation as an additional driving force for the mobile phase. The advantages of the new method were analyzed; the velocity coefficient of the movement of the mobile phase front was found to be linearly dependent on the rarefaction at the end of the plate.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1143–1146, May, 1996.     

Preparation and evaluation of 3 m open tubular capillary columns with a zwitterionic polymeric porous layer for liquid chromatography

A 3 m zwitterionic polymeric porous layer open tubular column (3 m × 25 μm id × 375 μm od) with a polymeric porous layer thickness of 4 μm was fabricated by the copolymerization of [2‐(methacryloyloxy)ethyl] dimethyl‐(3‐sulfopropyl) ammonium hydroxide and N,N’‐methylenebis(acrylamide). The effects of the diameter of the capillary, reaction temperature, and polymerization time on the preparation of the open tubular column were investigated. Characterized by scanning electron microscopy, the zwitterionic layer was observed to be rough and throughout the fused‐silica capillary homogenously, which increased the phase ratio. The separation of neutral, basic, and acidic compounds demonstrates the strong hydrophilicity of the poly[2‐(methacryloyloxy)ethyl] dimethyl‐(3‐sulfopropyl) ammonium hydroxide coating. In addition, the poly[2‐(methacryloyloxy) ethyl] dimethyl‐(3‐sulfopropyl) ammonium hydroxide porous layer open tubular column was applied for the analysis of flavonoids from the rootstalk of licorice, revealing the potential in separating complex samples. The relative standard deviation of retention time for run‐to‐run (n = 5), day‐to‐day (n = 3), and column‐to‐column (n = 3) of toluene, N,N‐dimethylformamide, formamide, and thiourea were below 1.2%, exhibiting good repeatability.     

Computational modeling of porous medium inside a channel with homogeneous nanofluid

Journal of Thermal Analysis and Calorimetry - In the present study, the flow field and heat transfer have been simulated numerically inside a channel. The channel is under the constant heat flux....     

Pulse microcatalytic setup with a reactor inside a flow calorimeter

A pulse microcatalytic setup, whose reactor is placed inside a Thiane-Calvet microcalorimeter is suggested. This setup permits to carry out simultaneous measurements of thermal effect and kinetic parameters of heterogeneous catalytic experiments during one experiment.

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Continuous flow thin layer headspace (TLHS) analysis

Summary A new method is presented for the continuous determination of volatile organic halogen (VOX) in water. It is based on isolation of the volatile analytes (VA) from the aqueous sample by means of the thin-layer headspace (TLHS) technique, mineralization of the VA in an empty quartz tube, and subsequent determination of the formed halogen ions absorbed in a liquid sorbent by means of an indirect spectrophotometric method using the iron thiocyanate complex. The method proved to be selective; no interferences of other elements at the levels encountered in practice have been found. Due to this fact and to the sensitivity of the method (of the order of 0.1 g/g) it is well suited for the determination of the VOX level in waste waters. The theory of the continuous flow TLHS analysis has been further developed. The results of mathematical analysis of the derived general equation for the concentration of the VA in the liquid sorbent are presented.Part I see [1]     

Continuous flow thin layer headspace (TLHS) analysis

Summary The paper presents a new method of a continuous isolation and determination of volatile organic halogens (VOX) in drinking waters based on so-called thin layer headspace (TLHS) isolation technique. The liberated volatile compounds are mineralized in an empty quartz tube at 850°C and absorbed in a buffered washing solution. After separation of air the halogen ions are determined potentiometrically in a flow-through cell using a silver/silver choride indicating electrode. The potential of the electrode is a linear function of the halogen ion concentration in the washing solution within the VOX concentration range usually encountered in drinking waters. The estimated detection limit of the method is ca. 0.1 g/l VOX and can be further improved by increasing the concentration factor. The theory of the TLHS isolation method has been further developed and verified. The derived dependences enable a simultaneous determination of the effective partition coefficients in the system, thus enabling calculation of the optimal gas flow rate.Part I and II, see [1, 2]     

Continuous flow thin layer headspace (TLHS) analysis

Summary The theoretical basis of the optimization of the TLHS analysis has been further developed. A critical value of the enrichment factor (F_{cr, inf}) has been defined as the value, at which the relative systematic error and the relative precision error are equal. These errors have been defined with respect to the maximum and the inflexion point of the recovery curve of the volatile analyte in the liquid sorbent. Two methods of volatile organic halogen (VOX) determination in tap water, viz. the conductometric and the indirect potentiometric method, have been compared (with respect to their analytical characteristics) using natural samples. The accuracy of both methods proved to be similar, yet the conductometric method was more precise. The variances of the methods occurred to be homogeneous in the particular measuring series independently of the long time intervals between the particular measuring series and the differentiated VOX levels.Part IV see [4]